Hammer impelling means in high speed printers



F. H. SHEPARD, JR

HAMMER IMPELLING MEANS IN HIGH SPEED PRINTERS Filed Jan. 22, 1955 April 2, 1957 2 Sheets-Sheet 1 ,qTToPNE) INVENTOR. EMA/0s M SHEMPD JP. kw

HAMMER IMPELLING MEANS IN HIGH SPEED PRINTERS Filed Jan. 22, 1955 April 2, 1957 F. H. SHEPARD, JR

2 Sheets-Sheet 2 I; l l l I i INVENTOR. Ewe/s SHEPflED 7E. &2M,

m um l m mf United States Patent HAMMER IMPELLING MEANS IN HIGH SPEED PRINTERS Francis H. Shepard, Jr., Madison, N. J. Application January 22, 1953, Serial No. 332,711 10 Claims. (Cl. 101-93) My invention relates to a high speed printer and more particularly to a hammer assembly for high speed printers.

Coding devices are known to the art whereby messages can be coded on perforated paper strips, magnetic tape or the like. These coding devices have a typewriter-like keyboard by which an operator may encode an appropriate record with the words, sentences, paragraphs and pages of any desired information. The record may be employed, as is known in the art, to transmit this information as a series of pulses over any known communication channel, such as radio, telephone or Wire. A decoder at the reception point then generates proper signals for operating a writer or printer. These systems are sometimes generically referred to as teletypewriter systems. The teletypewriter systems of the prior art have one major drawback in that the speed of printing is limited. This entails long transmission times, which represent a large expense in the operation of the transmission channel. A record can be made over a period of time containing a large amount of information. If this record could be printed rapidly without respect to the time required for making it, large savings could be made in transmission costs. Furthermore, a single channel could be used to transmit greatly increased quantities of in formation.

One object of my invention is to provide a high speed printer.

Another object of my invention is to provide a hammer assembly for high speed printers for cooperation with a continuously rotating type drum.

Another object of my invention is to provide a hammer assembly for a high speed printer in which the time of dwell of a hammer can be accurately controlled to within narrow limits.

Other and further objects of my invention will appear from the following description.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

Figure 1 is the top plan view of a hammer assembly forming part of my invention.

Figure 2 is a sectional view taken along the line 22 of Figure 1 showing the position of the type drum.

Figure 3 is a view of the portion of Figure 2 drawn on an enlarged scale.

Figure 4 is a sectional view taken along the line 4-4 of Figure 3.

Figure 5 is a fragmentary sectional view drawn on a smaller scale showing a modified arrangement of the hammer assembly.

' In general my invention contemplates the provision of a drum carrying a plurality of rings of type which is adapted to be rotated continuously above the hammers of my hammer assembly. Each hammer is controlled by a signal generated by a decoder. The encoding of the information, its transmission, the construction of the 2,787,210 Patented Apr. 2, 1957 decoder and the timing of the decoded signal form no part of this invention, are known to the art and are therefore not shown and described. Any appropriate decoding means known to the art may be employed to generate the actuating signals. The decoded signals are adapted to fire Thyratrons, the output of each of which energizes an electromagnet. The electromagnet attracts an armature which is adapted to impart momentum to a hammer positioned below the type drum. The hammer thus flies upwardly under the influence of the energy imparted to it by the armature, as a projectile. The phasing of the motions are such that each hammer will strike a predetermined letter carried by the moving type drum. An inked ribbon is positioned between the type and a paper upon which the message is to be printed, the hammer striking the back of the paper.

The mass of each hammer is quite small with respect to the mass of the drum, so that for all practical purposes we may consider the type drum as having infinite inertia. It is highly important in a printer that each of the letters be printed with the same pressure or force if an evenly typed or printed line is to appear in a finished copy. Furthermore, since the drum is continuously rotating, the dwell of the hammer must be through a comparatively short period of time if smearing or smudging is to be avoided. This is especially true with a high speed printer where the type drum is revolving rapidly and continuously.

The drum is made of any appropriate material such as metal and the type is made of a hard elasticmaterial such as beryllium copper. The hammers are made of any appropriate elastic material as for example tool steel. Neglecting the presence of the ribbon and the paper, let us consider the action when the hammer strikes the type. Since the mass of the hammer is low and both the type and the hammer are made of elastic material, and assuming that the coefi'icient of restitution is unity, the velocity of approach of the hammer will be equal to the velocity of its separation from the type. Stated otherwise, assuming that there are no losses, the momentum of the hammer approaching the drum will be equal to the momentum of the hammer leaving the drum. There will be an interval of time elapsing between the instant the hammer strikes the type and the instant the hammer leaves the type, or a period of dwell. This period of dwell cannot be Zero, since in such event the force imparting the momentum of separation to the hammer would be infinite, since the momentum is achieved by a force acting through a period of time. Stated differently, if the period of dwell is long, the force is correspondingly low, since the momentum of the hammer will be substantially constant after leaving the armature. Accordingly, by controlling the period of dwell, I can control the force or the pressure with which the hammer prints. By making the period of dwell longer, I print with less pressure than I print when the period of dwell is shorter.

When the hammer strikes the type drum, a compressional shock Wave longitudinal of the axis of the hammer, that is, along the axis of travel of the hammer, is created. This compressional shock wave travels along the lengtth of the hammer, is reflected from the interface between the end of the hammer and the air and then becomes a tensional shock Wave which travels longitudinally back along the hammer until it reaches the interface between the end of the hammer and the type drum. When this happens, the hammer is lifted from the type drum. The velocity of travel of the shock waves, which are waves of acoustic or mechanical energy, depends entirely upon the material of which the hammer is made. This velocity of travel remains the same irrespective of the amplitude of the shock wave. This is analogous, for example, to the travel of sound waves in air. A Whisper will travel at precisely the same velocity as does a cannon shot. Accordingly, the velocity imparted to the hammer and its mass, that is, the momentum of the hammer at the instant it is arrested has no influence upon the time of dwell. The time of dwell, therefore, is solely a function of the material of the hammer and its configuration. If the hammer is made longer, it will take a correspondingly longer time for the shock wave to travel from one end of the hammer to its opposite end. If the hammer is made shorter in length, the time of travel will be correspondingly lessened. It is understood, of course, that the mass of the hammer and its velocity do have a bearing upon the pressure of printing. With a higher velocity and a larger mass for the hammer, that is, for a larger hammer momentum, longer dwell will be required to print with a predetermined pressure. This phenomenom is an application of Newtons second law, namely, that the change of momentum is proportional to the impressed force and to the time during which it acts. This can be expressed by the equation where m is the mass, v is the terminal velocity, v is the initial velocity, 23 is time and F is the force acting. It will be seen from this equation that the force is directly proportional to the momentum and inversely proportional to time. Accordingly, for a given momentum, the force or the pressure in the instant case with which the hammer prints, can be varied by controlling the time through which the force acts. This time is the period of dwell during which the hammer prints.

In use, the hammer strikes a cushion comprised of the inked ribbon and the paper and, in some cases, of several sheets of paper with interleaved sheets of carbon paper. The ribbon and the paper are not elastic. Accordingly, some of the momentum of the hammer will be lost and converted into heat in deforming the nonelastic material between the hammer end and the type. The amount of energy lost, however, is small so that the pressure of printing is not appreciably varied. The loss of momentum, as pointed out above, however, does not affect the time of dwell. It merely reduces the amplitude of the shock wave.

More particularly, referring now to the drawings, an appropriate framework carries a hammer guide plate 12 which is secured thereto by screws 14. The guide plate is formed with a transverse slot 16, the edges of which are formed with a plurality of vertically extending guideways 18, in which I position a plurality of hammers for vertical movement in the guide slots. A cover plate 22 is adapted to be placed over the top of the assembly and is provided with a transverse slot 24 through which the hammers are adapted to fly on the Way upward to contact the type carried upon the type drum. This drum 26 is, as can be seen by reference to Figures 2 and 3, mounted with its axis of rotation positioned in a common vertical plane above the longitudinal axes of the slots 16 and 24. The type drum carries a plurality of type characters 26 which are spaced around the periphery of the drum along the locus of a circle formed by the intersection of the periphery of the drum with a vertical plane perpendicular to the axis of rotation of the drum. The type characters form a complete font of type. In practice I use only capital letters, nine numerals and five additional characters, making forty characters in all. The 0 serves for a zero. This gives me forty characters in a ring of type. The drum 26 is continuously driven by any appropriate synchronous motor (not shown). In practice I drive the drum at a speed of eighteen hundred revolutions per minute. The dwell of the hammers is adjusted to the order of fifty to sixty microseconds, i. e. twice the length of the hammer measured in time of acoustic wave propagation from one end I to the other.

.This dwell will produce a slight smudge during the printing which is not noticeable, being to the order of ten to eleven thousandths of an inch. The frame It) carries a pair of electromagnet-supporting plates 30 and 32, disposed on each side of the hammer guide plate 12. A plurality of electromagnet assemblies 34 are carried by the plates 39 and 32, being secured thereto by appropriate screws 35. There is one electromagnet assembly 34 for each ring of type. It will readily be understood that as many rings of type as may be convenient may be mounted on the drum 26. In a typical case I may have 120 rings of type. The spacing of type is determined by the width of the electromagnet assembly.

In order to space the type sufliciently close to avoid making the drum too long and to avoid increasing the space between letters of a word in the printed matter, I stagger the electromagnet assemblies, placing them on opposite sides of the hammer slot as can readily be seen by reference to Figure 2. The armature 36 of the left-hand elec tromagnet 34 in Figure 2 is adapted to strike a hammer 20. The armature 36 of the right-hand electromagnet assembly 34 is adapted to strike the adjacent hammer. In this manner the armatures on one side of the hammers actuate alternate hammers and the armatures on the other side of the hammer assembly actuate the intermediate hammers.

Each hammer 2G rests upon flanges .38, as can be seen by reference to Figures 2 and 3. These flanges contact the upper surface 40 of the hammer guide plate 12. Each armature 36 of the electromagnet assemblies is pivoted around pin 42 secured to the magnet frame 44. The frame carries a pair of electromagnets 46, the poles 48 of which are positioned adjacent the armatures 36. Each armature 36 is biased to move away from the pole pieces by a spring 50. An adjustable stop screw 52 carried in an internally threaded bore in plate 54 limits the downward movement of the armature 36. The windings of the electromagnets 46 are adapted to be energized through a pair of conductors 56 and 58 which are connected across the output terminals of the actuating circuit. It will be understood that there is a separate actuating circuit for each electromagnet controlled by the signals from the decoder. The clearance between the upper end of the hammer 20 and the face of the type 28 may be of the order of four hundredths of an inch. The armature 36 may, if desired, contact the lower end of the hammer 20. In practice I provide a clearance of the order of twenty-five thousandths of an inch. The clearances must be carefully adjusted so that the timing or phase of the operation is accurate. I have found, for example, that with a type drum having forty characters, the actuating signal should occur when the letter to be printed is three letters away from printing position. Since there are forty characters in the type drum and the drum is revolving at eighteen hundred revolutions per minute, the hammer must traverse the gap and strike the type in one four-hundredth of a second. If the hammer prints too soon, the gap between the end of the armature 36 and the bottom of the hammer is increased. If the hammer prints too late, this, gap is decreased. If the hammer prints with too much pressure, the length of the hammer is increased slightly to increase the period of dwell. If the hammer prints with too little pressure, the length of the hammer is slightly decreased to decrease the dwell until the proper printing pressure is achieved. As pointed out above, the decreasing of the length of the hammer decreases the length of dwell and correspondingly increases the printing pressure.

In use, a roll of paper 60 is intermittently fed across the top of the cover plate 22 in a direction transverse of the slot 24. The paper is stationary for the printing interval. This printing interval may be as short as one thirtieth of a second with a drum revolving at eighteen hundred revolutions per minute. If desired, the printing cycle may com-, prise two revolutions of the drum. Normally, a period of three revolutions of the drum is employed as the printing cycle. The information is fed continuously to the decoder during one cycle for use in the next printing cycle. As the drum rotates, the decoder produces actuating signals to cause predetermined hammers to fly upwardly to print when a predetermined character is 1n POSI- tion. All like characters in a complete line of type are advantageously printed at the same instant. Since all characters will be in position sometime during a complete revolution, a complete line may be printed during one revolution of the drum. During the second revolution of the drum, the paper and an inked n'bbon 62 are fed, and the ribbon feeder may be operated from the mechanism (not shown) which feeds the paper. Any appropriate means for feeding the ribbon and the paper and the timing of feeding the ribbon and the paper known to the art may be employed.

While the hammers may be placed closely adjacent to each other, the electromagnets require more width. If it is desired to place the characters closer to each other on the type drum, the arrangement shown in Figure 5 may be employed. In this arrangement a second bank of electromagnets 64 is supported in any appropriate manner below the upper bank of electromagnets 44. The hammer 20, actuated by an electromagnet of the lower bank, is not actuated directly from its armature 66 but through a transmitting member 68. The mass of each transmitting member 68 is equal to the mass of each hammer 20. The sum of the gap 70 between the lower end of the hammer 20 and the upper end of the transmitting member 68, the gap between the upper end of the hammer 20 and the type character 28 and the gap 72 between the lower end of member 68 and the armature 66 of the assembly shown in Figure 5 is equal to the sum of the gaps between the upper end of hammer 20 of an upper bank and its corresponding type 28 and the gap between the lower end of a hammer 20 of an upper bank and its armature 36. The armature 66 of a lower bank will impart energy to a member 68. It will fly upwardly and move the hammer 2t] upwardly as a projectile. Since both the hammer 20 and the member 68 are made of elastic material and have the same mass, the hammer 20 will move with the same velocity as the member 68 moved. The action of the parts is analogous to that of a cue ball hitting a billiard ball. The one ball will stop and impart its momentum to the billiard ball. The member 68 will stop and impart its 6 of the control of the time of dwell, I am enabled to control the printing pressure in an approved manner.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details Within the scope of my claims without departing from the spirit of my invention. It is therefore to be understood that my invention is not to be limited to the specific details shown and described.

Having thus'described my invention, what I claim is:

1. In an electro-mechanical printer of the character described, a hard, round type wheel having type characters around its rim and adapted to be rotated at. very high speed, means to move a strip of paper-like material to be printed upon tangentially past the rim of said wheel as it is rotating, a small, light-weight, elongated, hammer of hard, elastic material adapted to be fired against said paper-like material to force it against a desired one, but only one at a time, of the characters carried on the rim of said wheel, and electro-mechanical means to accelerate said hammer as a substantially free projectile against said paper-like material to set up an acoustic shock Wave traveling lengthwise in the hammer, the length of said hammer measured in time of acoustic wave propagation through it being substantially half the total desired dwell time of said hammer against said paper-like material and said wheel, whereby a blow of accurately controlled and even duration and force is obtained.

2. The method of imparting a short, sharp hammer blow to a medium to be struck for some purpose and which should not be damaged and wherein the hammer blow is controlled to have a finite and predetermined duration or dwell time and a force of approximately constant magnitude during said dwell time, said method comprising the steps of taking a small, relatively light-weight, elongated hammer of a hard, elastic material; bringing said hammer, lengthwise end first, relatively toward a medium having a hard surface of impact; suddenly impacting said hammer and said medium against each other thereby genmomentum to the hammer 20. The material of neither 1 the member 68 nor the hammer is deformed beyond its elastic limit. The period of dwell and the printing force,

'of course, in the form of the invention shown in Figure 5,

are again controlled by the dimensions and shape of the hammer 20. The arrangement in Figure 5 enables me to mount the printing hammers more closely adjacent each other. This reduces the space between the letters of the printed material and enables me to shorten the length of the type drum or alternately to print more characters fora given length of type drum.

Assuming that the printing cycle is one fifteenth of a second (two, one-thirtieth-of-a-second drum revolutions) and that I employ 120 rings of type, I can print 120 characters in one fifteenth of a second. Let us consider that the average word contains five characters and that there is one space between each word. With this measure I print twenty words in one fifteenth of a second or three hundred words a second. At this rate, I print eighteen thousand words per minute which, it will be recognized by the art, is a phenomenally high speed of printing. This speed of printing :can readily be increased by increasing the speed of rotation of the drum.

It will be seen that I have accomplished the objects of my invention. I have provided a high speed printer and more particularly, a hammer assembly for high speed printers adapted to cooperate with a continuously rotating type drum. By means of my invention, I am enabled to control the time of dwellof each hammer within narrow limits in a simple and accurate manner. By means erating an acoustic or mechanical shock wave traveling away fromthe surface of impact; allowing said hammer to dwell against said surface; reflecting at least a portion of the energy of said shock wave back toward said surface a predetermined time after impact of said hammer; and utilizing the energy in said reflected shock wave to move said hammer and said medium out of contact with each other; whereby the total time of dwell of said hammer is substantially twice said predetermined time and, though finite, can be made very short, and the force of contact of said hammer against medium is approximately constant during said dwell time.

3. The method as in claim 2 in which said shock wave is propagated lengthwise in said hammer and is reflected back from the far end thereof to cause the hammer end in contact with said medium to move out of contact therewith at the end of said dwell time.

4. A method of imparting a short, though finite duration, sharp hammer blow to a medium to be struck for some purpose and which together with the hammer should not be damaged by the blow, comprising the steps of taking a light-weight, long, thin hammer of a hard elastic material, moving said hammer with a finite velocity end first toward a hard medium having much higher inertia than said hammer, causing said hammer to strike said medium at a surface of impact and to generate a compressional shock wave of substantial amplitude traveling away from said surface in said hammer along its length, allowing said hammer to dwell against said surface, reflecting at the far end of said hammer at least a substantial portion of the energy in said compressional shock wave back toward said surface of impact as a tensional shock wave, and utilizing the energy in said tensional shock wave to move said hammer and medium out of contact whereby the 7 total dwell time of contact between hammer and medium is precisely determined and the force of contact of the hammer against the medium acts at least approximately uniformly during said dwell time and denting and flattening of the medium or the hammer as a result of repeated blows is made negligible.

5. The method as in claim 4 when it is desirable to have a .certain short dwell time for the hammer but yet desirable to act, in moving it against the medium, at a distance from the medium appreciably greater than the total length of the hammer, in further combination, the step of taking a second hammer like the first hammer, and moving said second hammer lengthwise against the far end of the first hammer to drive it by a cue ball effect against said medium, whereby the dwell time of said first hammer is determinedby its length alone rather than by the combined lengths of said first and second hammers together.

6. In a high-speed mechanical typewriter, at least one light-weight elongated hammer of hard, elastic material and which is a good propagator of acoustic or mechanical compressional and tensional wave energy, a strip having at least one layer of thin paper-like material suitable for printing upon and positioned opposite the near end of said hammer, a base member of a hard material positioned closely behind said strip opposite said hammer, means to advance said strip and said base member relatively past each other, and energizing means to bring the near end of said hammer against said stnip and into sudden impact with said base member over a surface of contact with a controlled momentum, said energizing means permitting said hammer and base member to dwell in contact with each other with said strip therebetween and to thereafter move out of contact with each other primarily under the action of the shock wave which is originated upon impact of said hammer and base member and is reflected back from the opposite end of said hammer to the surface of impact, the physical length of said hammer from said near to said opposite end measured in time of acoutic wave propagation being substantially half the desired total dwell time of said hammer against said base member, said dwell time being determined by said length, whereby up to a number of layers of said strip can be printed upon at very high speed by blows of said hammer against said strip and said base member, but the danger of cutting or puncturing said strip is minimized by the force and duration of said blows being controlled.

7. The combination of elements as in claim 6 in which said energizing means includes for each hammer an electromagnet having a pivoted armature, said armature at 8 itsfree end being positioned slightly behind across a. hair row but finite gap from an end of said hammer adapted when said electromagnet is energized to move forward into contact with said end of said hammer to accelerate it along its length forward for .a short distance and then to permit said hammer to continue to move forward as a substantially free projectile toward said base member, wherein said base member has effectively infinite inertia relative to that of said hammer and is substantially as hard as said harrnner, and wherein there are a plurality or": hammers all of approximately the same length adapted to be moved with substantially equal momentum whereby the marks printed by the various hammer blows will have substantially equal darkness or intensity.

8. The combination of elements as in claim 6 wherein said hammer is substantially homogeneous, is made of steel rod, and has a length of roughly 0.000025 second measured in time of acoustic wave propagation from one end to the other.

9. The combination of elements as in claim '6 wherein the net cross-sectional area of said hammer at one point is greater than at other points so that the mass of said hammer is lumped at points along its length.

10. The combination of elements as in claim 7 wherein each hammer has a fixed normal rest position independent of said armature in which position said hammer is spaced from said base member substantially exactly the same distance as every other hammer and wherein every hammer always travels from its same fixed position to strike said paper-like material.

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Potter Oct. 26, 1954 

